The biosynthesis of porphyrins and corrins will be studied by 13C, 1H, 2H and 3H NMR spectroscopy at the whole-cell and cell-free levels. The structures of intermediates will be determined. Large samples of 13C-labeled ALA and PBG will become available for studying porphyria, a disease caused by biochemical defects in the heme pathway. Mutants of P. shermanii which are deficient in B12 production are being examined to detect novel intermediates in the biosynthesis of the vitamin. The mode of action of coenzyme B12 which regulates the conversion of propionate to succinate via methylmalonyl-CoA mutase will be examined by direct NMR methods. The incidence of B12 deficiency in new born infants and adults, although rare, provides the rationale for understanding the molecular mechanism of the mode of action of B12 in mammalian systems. The work is expected to lead inter alia to the discovery of novel methods of monitoring metabolic processes in living cells and, eventually, human subjects, although the latter are not involved in this proposal. Within the five-year period of support requested, the understanding of vitamin B12 biosynthesis and the mode of action of coenzyme B12 should be considerably deepened at the molecular and mechanistic level.